U.S. patent number 4,072,592 [Application Number 05/618,103] was granted by the patent office on 1978-02-07 for radiation curable coating.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to George B. Due, John P. Guarino.
United States Patent |
4,072,592 |
Due , et al. |
February 7, 1978 |
Radiation curable coating
Abstract
A radiation curable coating composition for various substrates
containing an adduct of acrylic acid and an epoxy resin (which may
be modified with an anhydride, such as maleic anhydride), and a
reactive acrylate monomer vehicle. The coating composition can be
pigmented and can also contain additives commonly used in coatings,
such as wetting agents and flow control agents. The coating
composition does not require the usual hydrocarbon vehicles that
give rise to air pollution problems. Surface gloss of a UV cured
film obtained from a pigmented coating composition can be increased
by using a photosensitizer combination of 2-chlorothioxanthone and
a phenyl ketone, such as benzophenone. Adhesion of a cured coating
is improved by replacing the tertiary amine co-sensitizer, at least
in part, with dimethylaminoethyl acrylate.
Inventors: |
Due; George B. (Pittsburgh,
PA), Guarino; John P. (Trenton, NJ) |
Assignee: |
Mobil Oil Corporation (New
York, NY)
|
Family
ID: |
27043430 |
Appl.
No.: |
05/618,103 |
Filed: |
September 30, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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551584 |
Feb 20, 1975 |
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471412 |
May 20, 1974 |
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Current U.S.
Class: |
428/418; 427/514;
427/519; 428/413; 428/457; 428/473; 428/511; 430/281.1; 522/103;
522/14; 522/26; 522/40; 522/41; 522/45; 522/81; 523/400;
525/529 |
Current CPC
Class: |
C08F
299/026 (20130101); Y10T 428/31895 (20150401); Y10T
428/31678 (20150401); Y10T 428/31511 (20150401); Y10T
428/31529 (20150401) |
Current International
Class: |
C08F
299/02 (20060101); C08F 299/00 (20060101); C08F
008/00 () |
Field of
Search: |
;427/54
;204/159.15,159.18,159.14 ;260/836,837R,42.28 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tillman; Murray
Assistant Examiner: Page; Thurman K.
Attorney, Agent or Firm: Huggett; Charles A. Trigg; Hastings
S.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of copending
application, Ser. No. 551,584, filed Feb. 20, 1975, now abandoned
which is a continuation of application Ser. No. 471,412, filed May
20, 1974, now abandoned.
Claims
What is claimed is:
1. A radiation curable coating composition that comprises, by
weight of said composition, 10-75% of a diacrylate of a diglycidyl
ether of a bisphenol, or of a diacrylate of a diglycidyl ether of a
bisphenol further esterfied with 0.1-1 mole, per mole of said
diacrylate, of a dicarboxylic acid anhydride to form an esterified
product having an acid number of 10-40, and 25-90% of an ester of
acrylic acid.
2. The coating composition of claim 1, wherein said bisphenol is
bisphenol A.
3. The coating composition of claim 1, wherein said anhydride is
maleic anhydride.
4. The coating composition of claim 2, wherein said anhydride is
maleic anhydride.
5. The coating composition of claim 2, wherein said anhydride is
.DELTA.4-tetrahydrophthalic anhydride.
6. The coating composition of claim 1, wherein said ester is
hydroxypropyl acrylate.
7. The coating composition of claim 2, wherein said ester is
hydroxypropyl acrylate.
8. The coating composition of claim 3, wherein said ester is
hydroxypropyl acrylate.
9. The coating composition of claim 4, wherein said ester is
hydroxypropyl acrylate.
10. The coating composition of claim 1, wherein said ester is
hydroxyethyl acrylate.
11. The coating composition of claim 2, wherein said ester is
hydroxyethyl acrylate.
12. The coating composition of claim 1, wherein said coating is
curable by UV light and contains, by weight of said composition,
0.1-6% of a photosensitizer and 0-6% of a tertiary amine
co-sensitizer.
13. The coating composition of claim 12, wherein said
photosensitizer is 2-chlorothioxanthone and said tertiary amine is
methyldiethanolamine.
14. The coating composition of claim 8, wherein said coating is
curable by UV light and contains, by weight of said composition,
0.1-6% of 2-chlorothioxanthone and 0-6% of
methyldiethanolamine.
15. The coating composition of claim 9, wherein said coating is
curable by UV light and contains, by weight of said composition,
0.1-6% of 2-chlorothioxanthone and 0-6% of
methyldiethanolamine.
16. A coating composition of claim 11, wherein said coating is
curable by UV light and contains, by weight of said composition,
0.1-6% of 2-chlorothioxanthone and 0-6% of
methyldiethanolamine.
17. The coating composition of claim 1, wherein said coating is
curable by UV light and contains, by weight of said composition,
0.1-6% of 2-chlorothioxanthone and 0-6% of triethanolamine.
18. The coating composition of claim 2, wherein said coating is
curable by UV light and contains, by weight of said composition,
0.1-6% of 2-chlorothioxanthone and 0-6% of triethanolamine.
19. The coating composition of claim 1, wherein said coating
contains a pigment.
20. The coating composition of claim 1, wherein said coating
contains titanium dioxide pigment.
21. The coating composition of claim 6, wherein said coating
contains titanium dioxide pigment.
22. The coating composition of claim 9, wherein said coating
contains titanium dioxide pigment.
23. The coating composition of claim 12, wherein said coating
contains titanium dioxide pigment.
24. The coating composition of claim 14, wherein said coating
contains titanium dioxide pigment.
25. The coating composition of claim 15, wherein said coating
contains titanium dioxide pigment.
26. The coating composition of claim 16, wherein said coating
contains titanium dioxide pigment.
27. The coating composition of claim 18, wherein said coating
contains titanium dioxide pigment.
28. A substrate coated with the coating composition of claim 1.
29. A metal substrate coated with the coating composition of claim
2.
30. A metal substrate coated with the coating composition of claim
4.
31. A metal substrate coated with the coating composition of claim
9.
32. A metal substrate coated with the coating composition of claim
14.
33. A metal substrate coated with the coating composition of claim
21.
34. A metal substrate coated with the coating composition of claim
20.
35. A metal substrate coated with the coating composition of claim
22.
36. A metal substrate coated with the coating composition of claim
27.
37. The coating composition of claim 1, wherein said ester is a
carbamoyloxyalkyl acrylate.
38. The coating composition of claim 2, wherein said ester is a
carbamoyloxyalkyl acrylate.
39. The coating composition of claim 4, wherein said ester is a
carbamoyloxyalkyl acrylate.
40. The coating composition of claim 1, wherein said ester is
butylcarbamoyloxyethyl acrylate.
41. The coating composition of claim 2, wherein said ester is
butylcarbamoyloxyethyl acrylate.
42. The coating composition of claim 12, wherein said
photosensitizer is benzoin isobutyl ether.
43. The coating composition of claim 12, wherein said
photosensitizer is benzoin isopropyl ether.
44. The coating composition of claim 12, wherein said
photosensitizer is 4'-t-butyl-2,2,2-trichloroacetophenone.
45. The coating composition of claim 42, wherein said ester is
butylcarbamoylethyl acrylate.
46. The coating composition of claim 43, wherein said ester is
butylcarbamoylethyl acrylate.
47. The coating composition of claim 44, wherein said ester is
butylcarbamoylethyl acrylate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to epoxy acrylate ester coatings, for
substrates, that are curable with radiation.
2. Description of the Prior Art
British Pat. No. 1,241,851 describes a process for coating an
article that comprises applying a film of an ethylenically
unsaturated ester having hydroxyl groups and exposing it to
ionizing radiation. No liquid vehicle is used.
The coating composition of this invention comprises a similar resin
in a vehicle that is a reactive monomer. The vehicle, when the
coating composition is exposed to radiation and set, reacts with
the resin and becomes an integral part of the resultant
coating.
SUMMARY OF THE INVENTION
This invention provides a coating composition that comprises an
adduct of acrylic acid and an epoxy resin, or an anhydride modified
adduct, and a reactive acrylate monomer. A photosensitizer and
optionally, a tertiary amine co-sensitizer are used in the case of
ultraviolet (UV) light cured coatings.
It also provides a UV curable pigmented coating composition that
contains a photosensitizer combination of 2-chlorothioxanthone and
a phenyl ketone.
It further provides a UV curable coating composition that affords
improved film adhesion, in which at least part of the tertiary
amine co-sensitizer is replaced with dimethylaminoethyl
acrylate.
It still further provides substrates coated with the aforedefined
coating compositions.
DESCRIPTION OF SPECIFIC EMBODIMENTS
Prior practice has been to coat substrates, such as metals useful
for container manufacture, with a variety of coating compositions
comprising heat curable resinous components and non-reactive,
volatile organic solvents that are removed from the coating during
the curing process. Recent restrictions on allowable atmospheric
pollutants, the shortage of organic solvents, and the shortage of
fuels useful for firing curing ovens has created a need for coating
compositions which can be cured with lower energy requirements and
which eliminate the need for non-reactive organic solvents.
The coating compositions of this invention comprise an adduct, a
reactive monomer vehicle, and optionally a photosensitizer. The
adduct is an adduct of acrylic acid and an epoxy resin or said
adduct further modified by reaction with an anhydride.
The epoxy resin can be any polyglycidyl ether of polyhydric organic
compounds, especially polyhydric phenols. Particularly preferred
are the glycidyl ethers of bisphenols, a class of compounds which
are constituted by a pair of phenolic groups interlinked through an
intervening aliphatic bridge. While any of the bisphenols may be
used, the compound 2,2-bis (p-hydroxyphenyl) propane, commonly
known as bisphenol A, is more widely available in commerce and is
preferred. While polyglycidyl ethers can be used, diglycidyl ethers
are preferred.
Depending upon whether the epoxy resin is substantially monomeric
or polymerized to some degree, the preferred epoxy resins will have
an epoxy equivalent weight of between about 170 and about 2,000 and
an epoxy value between about 0.60 and about 0.05. The preferred
epoxy resins, i.e., those made from bisphenol A, will have two
epoxy groups per molecule. Accordingly, the stoichiometric amount
of acrylic acid to form a diacrylate adduct would be two moles of
acid for each two epoxy groups. In practice, however, it is
preferred to use slightly less acid than the amount necessary to
cover both epoxy groups to be certain that there is no free acrylic
acid remaining in the reaction product. Free acid would contribute
to excessive volatility of deposited films, while minor amounts of
free epoxy are not objectionable. Therefore, the amount of acrylic
acid reacted can be between about 1.85 moles to 2.0 moles of acid
per two epoxy groups. The esterification reaction between the
acrylic acid and epoxy resin is carried out at an esterification
temperature, e.g. between about 90.degree. C. and about 110.degree.
C. Esterification is continued until an acid number of 5-15 is
obtained. This reaction ordinarily takes place in 8-15 hours.
In another embodiment of this invention, the epoxy diacrylate is
further reacted with an anhydride. Maleic anhydride is preferred
but other anhydrides are contemplated for this purpose, such as
citraconic anhydride, succinic anhydride, ethylsuccinic anhydride,
amylenesuccinic anhydride, itaconic anhydride, glutaric anhydride,
.DELTA.4-tetrahydrophthalic anhydride, phthalic anhydride,
hemimellitic anhydride, trimellitic anhydride, and pyromellitic
anhydride. The amount of anhydride used will be between about 0.1
and about 1.0 mole anhydride per mole diacrylate resin. This
reaction is generally carried out at temperatures between about
80.degree. C. and about 90.degree. C. The reaction is considered
complete when the alcoholic KOH and aqueous KOH acid numbers agree,
i.e., about 10-40. This evidences a complete absence of anhydride
functionality.
The esterification reaction and the further reaction with anhydride
can occur without the aid of a catalyst. However, catalysts are
preferred such as tertiary amines; quaternary ammonium hydroxides,
such as benzyltrimethylammonium hydroxide; N,N-dimethylaniline;
N,N-benzylmethylamine; triethylamine; and KOH. It is also
advantageous to use small amounts of hydroquinone as a
polymerization inhibitor.
The epoxy diacrylate or the anhydride modified epoxy diacrylate,
prepared as aforedescribed, is then dissolved in a reactive monomer
vehicle to prepare the coating composition. The reactive monomer
vehicle contemplated herein is a monofunctional ester of acrylic
acid having from 4 to about 20 carbon atoms. The acrylate ester can
be an alkyl or hydroxyalkyl acrylate, such as methyl acrylate,
ethylacrylate, hydroxyethyl acrylate, propyl acrylate, isopropyl
acrylate, hydroxypropyl acrylate, butyl acrylate, isobutyl
acrylate, amyl acrylate, hexyl acrylate, octyl acrylate,
2-ethylhexyl acrylate, decyl acrylate, dodecyl acrylate, tetradecyl
acrylate, and hexadecyl acrylate. Also contemplated are the acrylic
esters of the well known class of ether alcohols having the
formula: ROCH.sub.2 CH.sub.2 OH, wherein R is C.sub.1 -C.sub.6
alkyl or phenyl, i.e. the Cellosolves. Examples of such esters are
methoxyethyl acrylate (Methylcellosolve acrylate), ethoxyethyl
acrylate (Cellosolve acrylate), butoxyethyl acrylate
(Butylcellosolve acrylate), isobutoxyethyl acrylate
(Isobutylcellosolve acrylate), hexoxyethyl acrylate
(Hexylcellosolve acrylate), and phenoxyethyl acrylate
(Phenylcellosolve acrylate). The contemplated reactive monomer
vehicle can be designated by the formula: CH.sub.2 =CHCOOR, wherein
R is C.sub.1 -C.sub.15 alkyl or hydroxyalkyl; C.sub.2 H.sub.4 OR',
wherein R' is C.sub.1 -C.sub.6 alkyl or phenyl; ##STR1## wherein R"
is C.sub.1 -C.sub.4 alkylene and R'" is C.sub.1 -C.sub.4 alkyl,
phenyl, or cresyl; ##STR2## wherein R'" is C.sub.1 -C.sub.4 alkyl,
phenyl, or cresyl; and ##STR3## wherein R" is C.sub.1 -C.sub.4
alkyl, R"" is H or C.sub.1 -C.sub.3 alkyl, and x is an integer from
1 to 10.
In the case above when R is ##STR4## the reactive monomer is a
carbamoyloxyalkyl acrylate. Compounds of this class are readily
prepared by well known methods for preparing carbamates. Thus, a
hydroxyalkyl acrylate, e.g., hydroxyethyl acrylate, can be reacted
with an isocyanate, e.g., butyl isocyanate, phenyl isocyanate, or
cresyl isocyanate to form the carbamoyloxyalkyl acrylate, in the
presence of a catalyst, e.g., dibutyltin dilauryl. Alternatively,
the carbamoyloxyalkyl acrylate can be prepared by first reacting a
hydroxyalkyl acrylate, e.g., hydroxyethyl acrylate, with phosgene
in the presence of a base to give a chloroformate intermediate and
then further reacting this intermediate with an amine, e.g.,
ethylamine, butylamine, or aniline, in the presence of a
tertiaryamine acceptor for HCl, e.g., triethylamine. Reference
should be made to U.S. Pat. No. 3,288,673 for a description of the
techniques involved, described therein with regard to forming
carbamates from hydroxybenzothiophenes.
When R is ##STR5## the reactive monomer is an alkyl 2-hydroxypropyl
ether acrylate. Compounds of this class are readily prepared by the
well known addition esterification reaction of acrylic acid with an
alkyl glycidyl ether, e.g. butyl glycidyl ether.
When R is ##STR6## the reactive monomer will be a polyoxyethylene
ether of alkyl acrylate. Generally, these compounds can be prepared
by reacting a hydroxyalkyl acrylate with an alkylene oxide
(1,2-epoxyalkane), e.g. ethylene oxide, 1,2-epoxypropane, or
1,2-epoxybutane, using a molar ratio of acrylate:alkylene oxide of
1:1 to about 10:1, at about 30.degree.-75.degree. C, and using an
initiator such as borontrifluoride etherate. In the specific case
wherein the alkylene and the alkyl groups are all ethyl, the
acrylate can be prepared by monoesterification of a
poly(oxyethylene) glycol (commercially available under the
registered trademark Carbowax) with acrylic acid or acryloyl
chloride.
Typical examples of carbamoyloxyalkyl acrylates, alkyl or aryl,
2-hydroxypropyl ether acrylates (alkoxy-2-hydroxypropyl acrylates),
and hydroxy polyoxyalkylene ethers of alkyl acrylates include
butylcarbamoylethyl acrylate, phenylcarbamoylbutyl acrylate,
cresylcarbamoylpropyl acrylate, butoxy-2-hydroxypropyl acrylate,
phenoxy-2-hydroxypropyl acrylate, cresoxy-2-hyroxypropyl acrylate,
hydroxy penta(oxypropyl) ether of ethyl acrylate, hydroxy
deca(oxyethylene) ether of butyl acrylate, and hydroxy
hexa(oxybutylene) ether of propyl acrylate.
The reactive monomer vehicle can contain a minor amount (up to
about 20 weight percent) of a polyfunctional acrylate, e.g.
neopentylglycol diacrylate, but it is predominantly monofunctional.
In some formulations, the reactive monomer vehicle may have
sufficiently high viscosity that it renders the formulation too
viscous for some applications. In such cases, it will be desirable
to control the viscosity by adding a more fluid vinyl monomer or
acrylate ester to the reactive monomer vehicle. Typically, the
addition of about 5 to 10 weight percent of a vinyl monomer, e.g.
N-vinyl pyrrolidone, to the reactive monomer vehicle can be
utilized to afford satisfactory viscosity control. Additionally, it
has been found that N-vinyl pyrrolidone increases the hardness of
the cured film.
The coating composition is cured by exposure to radiation. When the
radiation used is electron beam radiation a photosensitizer is not
needed, but when ultraviolet light is used, a photosensitizer is
needed. Suitable sensitizers include acetophenone,
4'-t-butyl-2,2,2-trichloroacetophenone,
4'phenoxy-2,2-dichloroacetophenone, benzophenone, xanthone, benzoin
isobutyl ether, benzoin isopropyl ether, and 2-chlorothioxanthone.
2-Chlorothioxanthone is preferred, particularly when the
formulation is pigmented. A tertiary amine co-sensitizer may also
be used in the UV curable coating formulation. It is not essential,
but it serves to speed up the cure rate. In order to realize this
function, it is necessary to have free amine present. Accordingly,
the amine concentration range when a co-sensitizer is used, is from
about 1.25 to about 3 times the amount required to neutralize free
acidity. The amount required for neutralization can be readily
calculated from the determined acid number of the resin. The
tertiary amines are normally liquid trialkylamines,
trialkanolamines, or tertiary mixed alkylalkanolamines.
Non-limiting examples of such amines are triethylamine,
triisopropylamine, tributylamine, trihexylamine,
tri-2-ethyl-hexylamine, tridodecylamine, methyldiethanolamine,
dimethylethanolamine, 2-hydroxyethyldiisopropylamine, and
triethanolamine.
The coating compositions described so far produce clear coatings
and are useful as such.
Although a pigment is not necessary, it is preferred to incorporate
a pigment into the coating composition of this invention. The
preferred pigment is titanium dioxide for white base coats, but any
well known filler pigment can be used, such as zinc oxide,
bentonite, silica, ochers, and chrome yellows or greens.
Depending upon whether the coating composition is pigmented or not,
the broad and preferred ranges of concentration of the components
are as set forth in the following Table I.
TABLE I ______________________________________ Broad, Wt. %
Preferred, Wt. % Not Not Component Pigmented Pigmented Pigmented
Pigmented ______________________________________ Adduct Resin 10-30
10-75 15-30 10-50 Reactive Monomer 40-60 20-90 30-50 50-90 Vehicle
Tertiary 0.5-6 0-6 2-4 0-4 Amine Sensitizer 0.1-6 0.1-6 0.5-1 0.5-5
(if used) ______________________________________
The coating composition is applied to a usual substrate, metal,
paper, leather, cloth, etc. using any of the usual methods of
application, including wiping, spraying and rollcoat application.
Suitable metallic substrates include aluminum, steel, and
tin-plated steel. The rate of application will be sufficient to
apply the coating at about 1-20 mg/sq. in. After application, the
coating is set by exposure to radiation for between about 0.01
second and about 30 seconds. In some cases, the coating will be set
by short exposure to radiation, e.g. less than one second, which is
sufficient to set the film so that it will accept inks and/or a
wet-ink varnish. Following the printing or varnishing opertion,
these coats may be further set by baking at about 250.degree. F. to
450.degree. F. for between about 3 seconds and about 5 minutes.
Suitable sources of radiation are ultraviolet light or electron
beam radiation. Preferably, an ultraviolet light of a wave length
below 4000 Angstrom Units is used. The electron beam radiation is
obtained from high energy electrons produced by high voltage
electron accelerator, resonant transformers, transformer
rectifiers, micro-wave waveguide linear accelerator, and
synchrotrons.
The following examples demonstrate the preparation of adducts and
coatings containing them, in accordance with this invention.
EXAMPLE 1
Using a vessel equipped with an agitator, a reflux condenser, an
inert gas inlet and a charging port, there was charged 660 grams
Epon 828. Epon 828 is a diglycidyl ether of bisphenol A having an
epoxy equivalent weight of about 185-192 and an epoxide value of
0.50-0.54. Through the gas inlet was introduced a nitrogen flow
which was maintained throughout the resin preparation cycle. While
under agitation, 238 grams glacial acrylic acid was added and
stirred until epoxy resin dissolved. Upon dissolution of the
acrylic acid, 1.3 grams triethyl amine and 0.1 gram hydroquinone
were added. Under continued agitation, heat was raised to
205.degree.-212.degree. F. and held at this temperature until an
acid number of 5-10 was obtained (approximately 10 hours).
Temperature was reduced to 150.degree.-160.degree. F. and 600 grams
hydroxypropyl acrylate was added and the mixture was stirred until
uniform. The final product was a clear solution of prepolymer in
monomer at a 60/40 weight ratio.
EXAMPLE 2
Using a vessel equipped as in the previous example, there were
charged 7200 g. Epon 828, 2590 g. glacial acrylic acid, 15 g.
triethyl amine and 1.2 g. hydroquinone. Agitation was started along
with nitrogen flow and the mixture was heated to 100.degree. C.
Temperature was maintained at 95.degree.-100.degree. C. until an
acid number of 5-10 was obtained; at this point, was added 432 g.
maleic anhydride and the temperature was held at 90.degree. C.
until the acid number, as determined by alcoholic KOH and aqueous
KOH, agreed, thereby indicating the complete absence of anhydride
functionality. The normal time for this phase of the resin
preparation was 1.5 hours. At this point, was added 6835 g.
hydroxypropyl acrylate. The final product was a 60/40 ratio of
preopolymer/monomer having a viscosity of 850-900 cp at 80.degree.
F. a weight/gallon of 9.5 pounds/gallon, and an acid value of
28-35. The molar ratio of maleic anhydride to epoxy resin was
0.25.
The following Examples 3 and 4 demonstrate coatings curable by
electron beam radiation.
EXAMPLE 3
In a suitable sized high speed disperser, were thoroughly mixed
27.1 pounds of the product from Example 1 and 42.8 pounds titanium
dioxide pigment and the mixture was stirred until a fineness of
grind of 7 or better was obtained. Then were added 31.4 pounds
hydroxypropyl acrylate, and 20.2 pounds of the product from Example
1 and the mixture was stirred until uniform. The resultant finish
had a pigment/binder ratio of 0.52/1 and a prepolymer/total binder
ratio of 0.4/1.
EXAMPLE 4
Using the equipment of Example 3, were thoroughly mixed 27.3 pounds
of the resin solution of Example 2, and 42.9 pounds of titanium
dioxide pigment. Continued high speed agitation until a fineness of
grind of 7 minimum was obtained. Agitation was continued but at
slower speed, while adding 10.0 pounds of resin solution of Example
2 and 17.5 pounds of hydroxypropyl acrylate. This was stirred until
uniform. The resultant finish had a pigment/binder ratio of 0.78/1
and a prepolymer/total binder ratio of 0.4/1.
EXAMPLE 5
To a suitable sized pebble mill, were charged one pound
2-chlorothioxanthone and 2 pounds hydroxypropyl acrylate. This was
ground for 24 hours, until thoroughly dispersed. The product is
suited for use as a photoinitiator for pigmented finishes.
EXAMPLE 6
In a suitably sized high speed disperser were thoroughly mixed 27.1
pounds of the product from Example 1, 42.8 pounds titanium dioxide
pigment, and 1.5 pounds of the product of Example 5. l This was
stirred until a fineness of grind of 7 or better was obtained.
Then, were added 31.4 pounds hydroxypropyl acrylate, 2.0 pounds
methyldiethanolamine and 20.2 pounds of the product of Example 1.
The mixture was stirred until uniform. The resultant finish had a
pigment/binder ratio of 0.52/1 and a prepolymer/total binder ratio
of 0.4/1.
EXAMPLE 7
Using the equipment of Example 6, were thoroughly mixed 27.3 pounds
of the resin solution of Example 2, 42.9 pounds of titanium dioxide
pigment, and 0.8 pounds of 2-chlorothioxanthone. High speed
agitation was continued until a fineness of grind of 7 minimum was
obtained. Agitation was continued but at slower speed while adding
10.0 pounds of resin solution of Example 2, 17.5 pounds of
hydroxypropyl acrylate, and 1.5 pounds of methyldiethanolamine.
This was stirred until uniform. The resultant finish had a
pigment/binder ratio of 0.78/1 and a prepolymer/total binder ratio
of 0.4/1.
EXAMPLES 8 through 27
In Table II are set forth data on various coatings prepared using
the techniques and methods set forth in Examples 1 through 7. Each
coating was applied to various substrates, cured by ultraviolet
light (UV) or electron beam (EB), and tested for film properties.
The adhesion test is carried out by cross-hatching a coated area
with individual score lines approximately 1/16 inch apart. Then
Scotch tape is firmly applied to the cross-hatched area and removed
with a quick snap. The amount of coating remaining on the panel is
observed visually and rated on a percentage basis. Pasteurization
is carried out by immersing the coated panels in water at
155.degree. F. for 30 minutes. Then, the panels are wiped dry with
an absorbent towel and the adhesion test is carried out as
aforedescribed.
In Table II, the following abbreviations are used:
______________________________________ 1004 = Epon 1004 Reaction
product epichlorohydrin and bisphenol A. M.W. about 1400, Epoxide
value 0.10-0.12. 828 = Epon 828 Diglycidylether of bisphenol A.
M.W. about 350-400. Epoxide value 0.50- 0.54. A = 2 moles acrylic
acid per mole epoxy M = .25 moles maleic anhydride per mole epoxy
HPA = Hydroxypropyl Acrylate HEA = Hydroxyethyl Acrylate 2-EHA =
2-Ethylhexyl Acrylate MDEOA = Methyldiethanolamine TEOA =
Triethanolamine cps = Centipoise Al = Aluminum CCO = Chrome-chrome
oxide treated steel CDC5 = #5 grade of tinplate steel TiO.sub.2 =
Titanium Dioxide THP = .DELTA. 4-Tetrahydrophthalic anhydride CTX =
2-Chlorothioxanthone Monomer = Reactive monomer vehicle UV-25 =
Ultraviolet light at line speed 25 ft./min per lamp. EB-2 =
Electron beam radiation at 2 megarad dosage
______________________________________
TABLE II
__________________________________________________________________________
VISCOSITY-ADHESION-GLOSS-LEVELING EFFECTS FOR VARIOUS LEVELS OF
EPOXY MOLE WEIGHT AND ANHYDRIDE
__________________________________________________________________________
Composition, Wt. % Viscosity cps at Resin Monomer TiO.sub.2 CTX
Amine shear rate Ex. Type Wt. % Type Wt. % Wt. % Wt. % Type Wt. %
222 sec.sup.-1 .0028 sec.sup.-1
__________________________________________________________________________
8 828/A/M 23.0 HPA 29.7 42 .5 MDEOA 4 615 18,000 9 828/A/M 23.2 HPA
34.8 42 -- -- -- 600 10,000 10 828/A/M 42 HPA 53 -- 1.0 MDEOA 4 200
200 11 828/A/M 44 HPA 56 -- -- -- -- 250 300 12 828/A 22.8 HPA 33.4
42 1.0 MDEOA 4 375 29,000 13 828/A 23.2 HPA 34.8 42 -- -- -- 400
60,000 14 828/A 53 HPA 44 -- 1.0 MDEOA 2 200 300 15 828/A 45 HPA 55
-- -- -- -- 150 200 16 1004/A/M 20 HPA 41.7 33.3 1.0 MDEOA 4 1000
2,460 17 1004/A/M 20 HPA 46.7 33.3 -- -- -- 1200 4,000 18 1004/A/M
30 HPA 66.5 -- .5 MDEOA 3 400 400 19 1004/A/M 30 HPA 70 -- -- -- --
500 600 20 1004/A 20 HPA 42.2 33.3 1.0 MDEOA 4 900 15,000 21 1004/A
20 HPA 46.7 33.3 -- -- -- 900 45,000 22 1004/A 30 HPA 66.5 -- .5
MDEOA 4 350 350 23 1004/A 30 HPA 70 -- 0 -- -- 450 550 24 828/A
23.2 HEA 30.3 42 .5 MDEOA 4 500 35,000 25 828/A 28.6 HPA 25.6 42
1.0 TEOA 2 1200 60,000 26 828/A/M 23.0 HPA/ 14.6/ 42 1.0 MDEOA 4
670 156,000 2-EHA 14.6 27 828/A/THP 23.2 HPA 30.3 37 .5 MDEOA 4 244
24,00
__________________________________________________________________________
Film Properties % Adhesion after % Adhesion after Cure bake,
5'-350.degree. F. Pasteurization 60.degree. Gloss Ex. Condition Al
CCO CDC5 Al CCO CDC5 % Leveling
__________________________________________________________________________
8 UV-25 100 100 25 100 100 0 30 Good 9 EB-2 100 100 25 100 100 0 90
Good 10 UV-25 100 0 0 100 0 0 80 Excellent 11 EB-2 100 0 0 100 0 0
95 Excellent 12 UV-25 100 0 0 100 0 0 50 Poor 13 EB-2 100 0 0 100 0
0 90 Poor 14 UV-25 0 0 0 0 0 0 80 Excellent 15 EB-2 0 0 0 0 0 0 95
Excellent 16 UV-25 100 100 100 100 100 50 60 Excellent 17 EB-2 100
100 100 100 100 50 90 Excellent 18 UV-25 100 100 100 100 100 0 80
Excellent 19 EB-2 100 100 100 100 100 0 90 Excellent 20 UV-25 100
100 0 100 100 0 55 Fair 21 EB-2 100 100 0 100 100 0 90 Fair 22
UV-25 100 0 0 100 0 0 80 Excellent 23 EB-2 100 0 0 100 0 0 90
Excellent 24 UV-25 100 100 25 100 100 0 55 Fair 25 UV-25 100 100 25
100 100 0 65 Good 26 UV-25 100 100 100 100 100 0 15 Fair 27 UV-25
100 100 100 100 50 0 60 Fair
__________________________________________________________________________
The results given in Table I indicate that:
(a) Increasing epoxy resin molecular weight improves adhesion to
metals.
(b) Maleic anhydride adducts have better adhesion to metals and
demonstrate better leveling than compositions containing resins
containing no maleic anhydride.
(c) Coatings containing TiO.sub.2 have better adhesion to metals
than do coatings of identical composition but without
TiO.sub.2.
In the foregoing examples of UV curable coatings, an amine
co-sensitizer was used. As indicated hereinbefore, the
co-sensitizer is not necessary and in clear coatings it causes a
discoloration that often is undesirable. In such a case, the amine
co-sensitizer is omitted and the amount of sensitizer is increased.
This is demonstrated in the following examples.
EXAMPLES 28 through 31
Coating compositions were prepared by admixing 40 weight percent of
the diacrylate of Epon 828 (Example 1), 55 weight percent of
hydroxypropyl acrylate, and 5 weight percent of a UV sensitizer. In
each example, a different sensitizer was used, namely, benzoin
isobutyl ether (BIBE); benzoin isopropyl ether (BIPE);
4'-t-butyl-2,2,2-trichloroacetophenone (BTA); and
4'-phenoxy-2,2-dichloroacetophenone (PDA). Each coating composition
was coated on aluminum at a film thickness of about 3 mg./in..sup.2
and exposed to a 2-lamp (200 watts/inch) UV light unit at 25 FPM
followed by a postbake of 3 min. at 350.degree. F. to remove
unreacted monomer. Each film was observed for film yield and
pertinent data are set forth in Table III.
TABLE III ______________________________________ Example Sensitizer
Film yield, % ______________________________________ 28 BIBE 85.6
29 BIPE 90.1 30 BTA 92.5 31 PDA 93.1
______________________________________
In the preceding examples, relatively short chain acrylate esters,
e.g., hydroxypropyl acrylate, were generally used. The following
examples demonstrate the use of other, longer chain acrylate
esters.
EXAMPLES 32 through 36
Coating compositions were prepared by admixing 40 weight percent of
the diacrylate of Epon 828 (Example 1), 55 weight percent of an
acrylate ester reactive monomer, and as sensitizer either 5 weight
percent BIBE or 5 weight percent BTA. In each composition, the
reactive monomer was (A) butoxy-2-hydroxypropyl acrylate, (B)
butylcarbamoylethyl acrylate, or (C) penta (oxyisopropyl) ether of
ethyl acrylate. Each coating composition was coated on aluminum and
cured as described in Examples 28-31. Pertinent data and film yield
results are set forth in Table IV.
TABLE IV ______________________________________ Example Monomer
Sensitizer Film yield, % ______________________________________ 32
A BIBE 85 33 A BTA 93 34 B BIBE 88 35 B BTA 96 36 C BTA 90
______________________________________
The coating compositions that have been described and illustrated
hereinbefore can be considered the "basic" coating compositions. It
has been found that certain properties of the cured film can be
markedly improved by incorporating additional chemicals into the
basic coating compositions.
With the basic UV curable coating compositions, the gloss of the
cured film is usually lower than desired, particularly at higher
cure rates. This gloss can be markedly increased by using in the
coating composition a sensitizer combination of
2-chlorothioxanthone and a phenyl ketone. Benzophenone is the
preferred phenyl ketone, but other phenyl ketones are contemplated,
such as acetophenone, propiophenone, and butyrophenone.
The following examples demonstrate this gloss improvement. In each
example, using the techniques and methods of Examples 1-7, a
pigmented coating composition (A) without benzophenone (Bzph) and
(B) with benzophenone were coated on aluminum and exposed to UV at
various cure speeds. The resulting films were tested for 60.degree.
gloss.
EXAMPLE 37
An epoxy diacrylate of Epon 828 was modified with 0.25 mole maleic
anhydride per mole epoxy. This resin (Resin A) was admixed with
hydroxypropyl acrylate, TiO.sub.2 pigment, and sensitizers and
co-sensitizers. The following tabulation sets forth amounts of
components, pigment/binder ratio (P/B), resin/binder ratio (R/B),
and pertinent test data.
______________________________________ Example TiO.sub.2 CTX MDEOA
Resin A ______________________________________ 37A 36.6 0.9 3.6
24.5 37B 36.6 0.9 3.6 24.5 Example HPA Bzph P/B R/B
______________________________________ 37A 34.4 0 .58 .39 37B 32.4
2.0 .58 .39 UV Cure Speed 25 FPM No Bzph 2% Bzph Yield 90 90 Gloss
79 88 ______________________________________
EXAMPLE 38
An epoxy diacrylate of Epon 828 (Resin B) was admixed with
hydroxypropyl acrylate, TiO.sub.2 pigment, and sensitizers and
co-sensitizers. The following tabulation set forth amounts of
components and pertinent test data.
______________________________________ Example TiO.sub.2 Resin B
HPA CTX ______________________________________ 38A 42.8 28.6 25.6
1.0 38B 41.5 27.7 24.8 1.0 Example MDEOA Bzph P/B R/B
______________________________________ 38A 2.0 0 .75 .50 38B 3.0
2.0 .71 .475 UV Cure Speed, FPM No Bzph 2% Bzph 25 Yield 94 91
Gloss 95 95 50 Yield 91 87 Gloss 77 93 100 Yield 87 84 Gloss 39 90
______________________________________
EXAMPLE 39
An epoxy diacrylate of Epon 1004 was modified with 0.25 mole maleic
anhydride per mole epoxy. This resin (Resin C) was admixed with
hydroxypropylacrylate, TiO.sub.2 pigment, and sensitizers and
co-sensitizers. The following tabulation sets forth amounts of
components and pertinent test data.
______________________________________ Example TiO.sub.2 Resin C
CTX ______________________________________ 39A 33.3 20.0 1.0 39B
33.0 19.8 1.0 Example MDEOA HPA Bzph
______________________________________ 39A 4.0 41.7 0 39B 4.0 41.2
1.0 UV Cure Speed, FPM No Bzph 2% Bzph 25 Yield 88 88 Gloss 89 89
50 Yield 86 85 Gloss 75 88 100 Yield 73 77 Gloss 45 62
______________________________________
The preceding examples illustrate that benzophenone (a phenyl
ketone) combined with 2-chlorothioxanthone has essentially no
effect on film yield, but increases the gloss of pigmented UV
curable coatings. Each sensitizer is used, as described
hereinbefore, in amounts of between about 0.1% and about 2% by
weight.
It has been found that adhesion of the cured coating to some
substrates, particularly pasteurized adhesion (Past. Adh.), is
improved by using dimethylaminoethyl acrylate (DMAEA) in the
coating composition. In the case of EB curable coatings, the DMAEA
is added to the coating composition in amounts of between about
0.5% and about 6% by weight. In the case of UV curable coatings the
DMAEA is used in amounts of between about 0.5% and about 6% by
weight to replace all or a part of the tertiary amine
co-sensitizer.
EXAMPLE 40
Resin B (Example 38) was admixed with hydroxypropyl acrylate,
2-chlorothioxanthone, and MDEOA or DMAEA. Each coating was coated
on aluminum panels and UV cured. The coated panels were subjected
to adhesion tests. Amounts of components and test results are set
forth in the following tabulation.
______________________________________ Example Resin B CTX HPA
MDEOA DMAEA ______________________________________ 40A 49.5 1.0
44.5 0 5 40B 50.0 1.0 47.0 2 0 50 FPM UV Cure Film Example Yield
Adhesion Past. Adh. ______________________________________ 40A 92
100 50 40B 89 20 0 ______________________________________
EXAMPLE 41
Resin C (Example 39) was admixed with hydroxypropyl acrylate,
2-chlorothioxanthone, and MDEOA or DMAEA. Each coating was coated
on aluminum panels and UV cured. The coated panels were subjected
to adhesion tests. Amounts of components and test results are set
forth in the following tabulation.
______________________________________ Example Resin C HPA CTX
MDEOA DMAEA ______________________________________ 41A 29.2 68.2
0.5 2 0 41B 29.2 68.2 0.5 0 2 UV Cure Speed, Film Past. Example FPM
Yield Adh. Adh. ______________________________________ 41A 25 92
100 85 50 87 100 70 41B 25 89 100 100 50 87 100 100
______________________________________
EXAMPLE 42
Resin B (Example 38) was admixed with hydroxypropyl acrylate,
TiO.sub.2 pigment, 1.0% 2-chlorothioxanthone, and MDEOA or DMAEA.
The P/B of each coating was 0.75 and the R/B was 0.40. Each coating
was coated on metal panels and UV cured. The coated panels were
subjected to adhesion tests. Results are set forth in the following
tabulation.
______________________________________ Viscosity, cp Example Amine
222 sec.sup.-1 .0228 sec.sup.-1
______________________________________ 42A 4% MDEOA 395 29,100 42B
5% DMAEA 283 564 50 FPM Adhesion to Example Yield Al CCO
______________________________________ 42A 89 100 0 42B 89 100 100
______________________________________
EXAMPLE 43
Resin B (Example 38) was admixed with hydroxypropyl acrylate,
TiO.sub.2 pigment, 1.0% 2-chlorothioxanthone, and MDEOA or DMAEA.
The P/B of each coating was 0.75 and the R/B was 0.6. Each coating
was coated on metal panels and UV cured. The coated panels were
subjected to adhesion tests. Results are set forth in the following
tabulation.
______________________________________ Example Amine 222 sec.sup.-1
.0228 sec.sup.-1 ______________________________________ 43A 4%
MDEOA 800 86,100 43B 5% DMAEA 598 14,800 50 FPM Adhesion to Example
Yield Al CCO ______________________________________ 43A 88 100 0
43B 89 100 100 ______________________________________
It will be noted from the preceding examples that the use of
dimethylaminoethyl acrylate gives at least equivalent UV cure. It
also provides improved adhesion, both dry and wet.
The following examples are illustrative of preferred coating
compositions of this invention.
EXAMPLE 44
Using a reaction vessel equipped with an agitator, a reflux
condenser, an inert gas inlet and a charging port, there were
charged 525 g. Epon 1004 and 70 g. toluene. Heat, agitation, and
slow inert gas flow were started. Temperature was raised to reflux
to remove water (a pot temperature of 150.degree. - 160.degree.
C.). The mixture was cooled to 80.degree. - 85.degree. C. and there
were added 40 g. glacial acrylic acid, 1 g. triethyl amine and 0.1
g. hydroquinone. Temperature was raised to 95.degree. - 100.degree.
C. for esterification and the reaction continued until an acid
number of 8-13 was obtained. This was cooled to 80.degree. -
95.degree. C. and there was added 7 g. maleic anhydride.
Temperature was held at 80.degree. - 85.degree. C. for 11/2 to 2
hours until alcoholic KOH and aqueous KOH acid numbers agreed
(10-15). Heat source was removed and 175 g. hydroxypropyl acrylate
was added. The mixture was reheated to 80.degree. - 85.degree. C.
and vacuum applied for toluene removal. Remove heat and add an
additional 182 g. hydroxypropyl acrylate. The final product had a
viscosity of 45-50,000 cp., a wt./gal. of 9.6 lb., an acid number
of 10.5 and a total solids of approximately 97%. This resin was
used in the formulations of Examples 45-47 (amounts are wt. % of
formulation):
______________________________________ EXAMPLES 45 - 47 (Clear
Finishes) Ingredient 45 46 47
______________________________________ Example 44 composition 40.3
56.4 33.2 Hydroxypropyl acrylate 56.3 40.2 37.6 Phenylcellosolve
acrylate -- -- 21.8 Methyldiethanolamine 1.9 1.9 2.9
Dimethylaminoethyl acrylate -- -- 3.5 2-Chlorothioxanthone 0.5 0.5
0.5 Fluorocarbon wetting agent -- -- 0.5 Silicone lubricant 1.0 1.0
-- Viscosity (seconds #4 Ford Cup) 50 - 60 175 - 225 30 - 35
Wt./gal. (lb.) 9.04 9.40 8.95
______________________________________
Examples 45 and 46 were formulated as an abrasion resistant coating
for can bottoms, which is applied by a wiping action and given a UV
treatment of 1-2 seconds with no post bake required.
Example 47 was formulated as a coating for flat sheet and is
suitable for rollcoat application and given 1 second exposure to UV
radiation, followed by a 10 minute oven bake at
340.degree.-400.degree. F. The Phenylcellosolve acrylate in Example
47 imparts improved corrosion resistance and flexibility.
EXAMPLE 48
There were charged 312 g. of an epoxy diacrylate made from Epon 828
and acrylic acid, 430 g. titanium dioxide, 198 g. Cellosolve
acrylate, 10 g. 2-chlorothioxanthone, 40 g. dimethylaminoethyl
acrylate and 10 g. benzophenone to a suitably sized pebble mill and
ground to a fineness of 7 when measured on a Hegman fineness of
grind gauge. Grind time is 24-48 hours. The final product was a
white finish suitable for rollcoat application on flat sheet. The
finish has a viscosity of 90-100 sec. #4 Ford Cup and a weight per
gallon of 13.1-13.3 pounds. It is normally applied at 10 mg./sq.
in. and cured using a 1 sec. UV exposure followed by a 6 minute
bake at 325.degree. F. After the UV exposure, the film was
sufficiently set to accept inks and a wet ink varnish. The 6 min.
at 325.degree. F. bake indicated above followed inking and
varnishing operations.
It will be noted that in Examples 47 and 48, dimethylaminoethyl
acrylate was used. This compound has a tertiary amine
functionality. Thus, as aforedescribed, it can replace the tertiary
amine (used to speed up the cure rate) partially (Example 47) or
entirely (Example 48). This compound also has reactive
ethylenically unsaturated functionality (acrylate) and therefore
acts as a reactive monomer. Its use affords a coating composition
having improved rheology, as evidenced by better flow
characteristics, and the cured coating has improved adhesion to
metal substrates. The addition of benzophenone to the coating
composition (Example 48) improves the gloss of the pigmented
finish.
Other well known adjuvants may be added to the coating composition
such as flow control agents and waxes. Waxes, if used, are added as
slurries or emulsions of petroleum (paraffin) wax, natural waxes
such as montan wax, beeswax, and carnauba wax, or synthetic waxes
such as polyethylene wax.
Although the present invention has been described with preferred
embodiments, it is to be understood that modifications and
variations may be resorted to, without departing from the spirit
and scope of this invention, as those skilled in the art will
readily understand. Such modifications and variations are
considered to be within the purview and scope of the appended
claims.
* * * * *